Three position apparatus have many applications. One of these applications is to use the three position apparatus as a transfer switch in an electrical power system. Such an electrical switch may be used to transfer from a normal power source to a backup power source, such transfers may occur when there is an interruption of normal power supply. The interruption of normal power supply may be caused by a variety of reasons: earthquake, flood damage, adverse weather conditions, or utility unreliability, for example. In the event that a normal power source, such as an electric utility, experiences an outage and fails, it is often necessary to supply critical and essential electrical needs by means of a standby electrical power system.
Often, the standby power supply system is an on-site electrical power source suitable to the needs of the applicable regulations and user criteria. The standby or emergency power supply system functions to provide a source of electrical power of required capacity, reliability and quality within a specified time after loss or failure of the normal power supply. The emergency power supply system varies depending upon the particular situation, for example, there may be a specified maximum time for which the load terminals of the transfer switch are permitted to be without acceptable electrical power. Quick transfer is especially important where critical equipment is involved, as in hospitals, airports and computer installations.
Accordingly, there is a need in the art for three position transfer switches that are able to handle a 400 Ampere bypass switch, able to make the transfer quickly, from about 20 milliseconds to about 100 milliseconds for example, have ease of operation, and are compact.